Technical Field
The present invention relates to a rotor having a first rotor portion and a second rotor portion, and to an electric rotating machine having the rotor.
Related Art
In order to reduce magnetic sound, the rotor of an IPM (Interior Permanent Magnet Motor) is divided into two stages in the axial direction, and the divided two stages are arranged being relatively deviated by ½ slot pitch angle. According to this configuration, pulsating components are offset in the torque waveforms generated in the first rotor portion and the second rotor portion.
In this regard, a patent document JP-B-4269953, for example, discloses an example of a technique related to an electric rotating machine which aims to more smoothly offset the pulsating components in the torque waveforms. In this electric rotating machine, the rotor is divided into three stages in the axial direction. Of the three stages (three rotor portions), a first rotor portion whose stack thickness is half of that of a second rotor portion is arranged at both ends, and the second rotor portion is arranged in between the first rotor portions, with the second rotor portion being deviated from the first rotor portions by ½ slot pitch angle.
However, application of the stage skew described in the patent document JP-B-4269953 raises the following problem. Specifically, when a magnetic field based on a predetermined current is applied to the rotor from the stator to generate torque, a magnetic field vector from the stator is generated at a position deviated from an optimum control lead angle by ½ slot pitch angle. In this case, the rotor arranged rearward with respect to the rotation direction is controlled on the basis of a lead angle advanced by ½ slot pitch. In a rotor having magnets and used for an IPM or an SPM (Surface Permanent Magnet Motor), the amount of demagnetizing field acting on the magnets is increased when the lead angle is advanced. As a result, the magnets are demagnetized, disabling generation of predetermined torque.